Various heat transfer recording methods have been known so far. Among these methods, dye diffusion transfer recording systems attract attention as a process that can produce a color hard copy having an image quality closest to that of silver halide photography. Moreover, this system has advantages over silver halide photography: it is a dry system, it enables direct visualization from digital data, it makes reproduction simple, and the like.
In this dye diffusion transfer recording system, a heat-sensitive transfer sheet (hereinafter also referred to as an ink sheet) containing dyes is superposed on a heat-sensitive transfer image-receiving sheet (hereinafter also referred to as an image-receiving sheet), and then the ink sheet is heated by a thermal head whose exothermic action is controlled by electric signals, in order to transfer the dyes contained in the ink sheet to the image-receiving sheet, thereby recording an image information. Three colors: cyan, magenta, and yellow, are used for recording a color image by overlapping one color to other, thereby enabling transferring and recording a color image having continuous gradation for color densities.
Recently, various printers allowing higher-speed printing have been developed and commercialized increasingly in the field of the dye-diffusion transfer recording systems. The high speed print enables to shorten a waiting time when a user obtains a print in a shop. For the foregoing reason, there is a demand for further speeding up of printing.
In order to prevent thermal sticking between a thermal printer head of a printer and a heat-sensitive transfer sheet and to give the thermal printer head and the heat-sensitive transfer sheet a slipping property therebetween, a heat-resistant lubricating layer is formed on the heat-sensitive transfer sheet surface contacting the thermal printer head. The thermal sticking occurs in a case where there is a break of the ink ribbon or the slipping property of the ink ribbon is insufficient when an image is printed, whereby image defects may be generated because the heat-sensitive transfer sheet is stretched or creased, or deformed into some other form at the printing time. According to high-speed printing, a thermal printer head comes to contact the heat-resistant lubricating layer at a higher temperature and a higher speed. Thus, the heat-resistant lubricating layer is desired to have even better performances.
For example, Japanese Patent No. 3,410,157 discloses a technique of incorporating a phosphate ester (also called phosphate or phosphoric ester) surfactant, which is excellent in lubricity, into a lubricating layer, and incorporating magnesium hydroxide and particles having a Mohs' hardness less than 3 as neutralizing agents into the layer in order to restrain corrosion or abrasion of a thermal printer head by decomposition of the phosphate ester. Moreover, JP-A-8-90945 (“JP-A” means unexamined published Japanese patent publication) discloses a technique of incorporating, into an inorganic filler contained in a heat-resistant lubricating layer, a hard impurity component in a certain amount range, thereby restraining creases or an abrasion of a thermal printer head.
The above-mentioned techniques have been used to investigate an improvement in performances of a heat-resistant lubricating layer in high-speed printing, so as to find out that the following cases may be caused: a case where the lubricity between a thermal printer head and the heat-resistant lubricating layer of a heat-sensitive transfer sheet is insufficient so that the heat-sensitive transfer sheet is not restrained from being deformed when an image is formed; and a case where refuses or residues adhering to a thermal printer head injure or damage the heat-sensitive transfer sheet when an image is formed, whereby the sheet is cut. The deformation of the heat-sensitive transfer sheet causes creases or other image defects when an image is printed; thus, the deformation is required to be overcome. Moreover, the cutting of the heat-sensitive transfer sheet causes an abnormal stop of the printer; thus, the cutting is also required to be overcome.